Refrigeration defrost control responsive to operation of condenser fan



Apnl 22, 1969 R. E. CHRISTMAN 3,439,511

REFRIGERATION DEFROST CONTROL RESPONSIVE TO OPERATION OF CONDENSER FAN Filed Feb. 29, 1968 T T Y DEFROST HEATER m COMPARTMEQJ'T 5O FEZ THERMOS A DRAIN HEATER- g JmmnhnL Lf 2 25 T EVAPORATOR M8 48 zofcqm ggg CONEENSER CONDENSER K IFQMPRESOR f E.j/RJN MOTOR I4 WITNESSES |NVENTOR WW Ralph E. Christmon ATTORNEY United States Patent Oflice 3,439,51 l Patented Apr. 22, 1969 US. Cl. 62-155 3 Claims ABSTRACT OF THE DISCLOSURE Refrigerator circuit arrangement in which a refrigeration-defrost control switch is driven by the condenser fan motor which is connected for energization through the refrigeration compartment thermostat to permit a period of compressor and compartment fan dormancy following defrost termination.

BACKGROUND OF THE INVENTION Field of the invention The invention pertains to the art of controlling refrigeration devices.

Description of the prior art It has been hertofore proposed to eliminate the usual separate timer motor used to control switch means for periodically effecting defrost of the refrigerator evaporator by instead driving the refrigeration-defrost control switch means directly from the motor driving the fan which circulates air over the evaporator and through the refrigerated compartment. One published example of such an arrangement is found in US. Patent 3,159,980 in which the duration of the defrost cycle is controlled by a dashpot arrangement so that a refrigeration cycle is not again initiated until the dashpot controlled time has expired. This dashpot technique has the inherent advantage of permitting the duration of the defrost cycle to be set in excess of the actual time required for completing the defrost of the evaporator. This allows the evaporator to cool somewhat before the compressor and compartment fan are again energized, and accordingly reduces the load upon the compressor when it again starts. This overage of time for a defrost cycle is conventional also in those arrangements in which a separate timer motor is used to control the defrost period, since the timer is typically set to allow a period of, say, 25 minutes for defrost, while the evaporator is typically defrosted in, say minutes. While as noted the dashpot arrangement does have the inherent advantage of permitting the setting of a duration of refrigeration system dormancy to exceed the actual time required for defrost, the dashpot arrangement may be considered to constitute a timer of sorts itself so that in effect one timer (the dashpot) has been substituted for another.

It has been proposed as an improvement of such an arrangement that the restoration of the refrigerationdefrost control switch means to a refrigeration position be effected immediately after the evaporator has been defrosted, with the operation of the compressor resuming, but not the operation of the compartment fan. That improved arrangement provides, as disclosed in Harbour US. patent application S.N. 671,686, also assigned to my assignee, that the compartment fan motor (which drives the refrigeration-defrost control switch between its alternate refrigeration and defrost positions at the expiration of selected accumulated times of fan motor operation), and the compressor motor, be shunted by a defrost thermostat during the defrost operation to prevent the energization of the compartment fan motor and compressor motor. Completion of defrost opens the defrost thermostat to momentarily energize the compartment fan motor through a completed circuit which includes the defrost heater, the fan motor and the compressor motor, to shift the control switch back to a refrigeration position. The high impedance of the compartment fan motorrelative to the compressor motor precludes any attempt of the compressor motor to start while the shifting of the switch takes place. Restoration of the control switch to the refrigeration position deenergizes the compartment fan motor and energizes the compressor motor. After. the compressor operation has pulled down the temperature of the evaporator to a level which causes the defrost thermostat to close, the compartment fan'is again energized.

In the preferred embodiment of the Harbour improved arrangement, which is particularly adaptable to larger size refrigerators, the condenser fan is connected in the circuit arrangement so that it operates independently of the refrigeration-defrost coritnol switch position. The result of this arrangement is that the condenser fan circulates air over the condenser during the defrost operation, and also over the compressor, so that lower condenser temperatures and lower compressor motor winding temperatures exist at restart. The lower condensing temperature promotes more rapid condensation of gas in the high side and therefore reduces the load against which the compressor must work. Of course the lower winding temperatures in the compressor motor also means lower winding resistance allowing the compressor motor to produce a higher starting torque.

SUMMARY OF THE INVENTION My invention departs in at least one material respect from the Harbour arrangement in that the refrigerationdefrost control switch is controlled by running time of the condenser fan rather than the compartment fan. In this arrangement it is mandatory that the condenser fan be connected in the circuit so that it is controlled solely by the compartment thermostat and is independent in operation from the compressor and compartment fan, as well as independent of the condition of the defrost termination thermostat. With this arrangement, there is no need to momentarily energize the compartment fan when the defrost termination switch opens to restore the defrost termination switch to a refrigeration position. Consequently, compressor operation can be delayed for a substantial period after defrost has been accomplished to give the different pressures in the system an opportunity to equalize so that the load against which the compressor must work upon restart is reduced.

Another advantage of this arrangement, in which return of the refrigeration-defrost switch to a refrigeration position is not dependent upon the opening of a defrost termination thermostat, is that a failure of the defrost termination thermostat in a 'closed position does not result in the defrost cycle continuing indefinitely, since the defrost termination thermostat is no longer than the key to restoring the device to a refrigeration cycle.

DRAWING DESCRIPTION The single figure is an electrical schematic and diagrammatlc representation of a refrigerator incorporating a circuit arrangement according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawing, the broken line outline 10 represents the storage compartment of the refrigerating device (hereinafter called the refrigerator), which may be a typical domestic refrigerator or freezer.

The refrigeration system includes the usual refrigeration components such as the refrigerant compressor 12 driven by motor 14, refrigerant condenser 16, and refrigerant evaporator 18. The refrigerant conducting conduits connecting the refrigerant components are omitted for clarity. Also, the drawing does not illustrate the specific locational relationships between the parts of the refrigeration system, although it is noted that the evaporator will conventionally be located in a passageway separate from the interior of the storage compartment with the compartment fan located to circulate air between the passage way and the compartment. The compressor 12 and its motor 14, along with the condenser 16 are conventionally located in the machine compartment of the refrigerator outside of the general confines of the storage compartment 10. These latter elements are physically located so that the condenser fan 22 creates a draft of air through the condenser and over the compressor and motor casing. The general direction of air flow created by the two fans 20 and 22 is indicated by the broken line arrows associated therewith.

The defrost heater 24 is disposed in heat exchange relation with the evaporator 18 in the noted separate passageway to effect its defrost. The defrost thermostat 26 is located so as to be responsive to the temperature condition of the evaporator. The defrost thermostat has a normally closed position in response to a temperature indicating a normal refrigerated condition of the refrigerator. Upon detecting a defrosted condition of the evaporator, the thermostat opens.

Other main components of the arrangement of concern in connection with the invention include the refrigerationdefrost control switch 28 which has a refrigeration position (solid line), and an alternate defrost position (broken line), between which positions the switch is periodically moved through a gear system after predetermined accumulated running times of the condenser fan motor 30. The storage compartment is provided with a compartment thermostat 32 which, under normal conditions, initiates and terminates the operation of the refrigeration system in accordance with variations in the compartment temperature above and below, respectively, the set point to which the thermostat is adjusted. The opposite sides of the electrical power source are identified at 34 and 36.

Operation Under normal refrigerating operation of the system, the compartment thermostat 32 closes in response to a compartment temperature calling for cooling. This completes a refrigeration producing circuit from the thermostat 32 through line 38, switch 28 in its refrigeration position, line 40 connecting one side of the compressor motor 14 to the switch 28, and line 42 connecting the other side of the compressor motor through a thermal overload motor protector 44 to the opposite side 36 of the power source. The compartment fan motor 46 is also energized at this time through the control switch 28 in its refrigeration position and line 40 connected to one side of the fan motor. The other side of the fan motor is connected to opposite side 36 of the power source. It will be appreciated that the defrost thermostat 26 is in a normally closed position due to the unde'frosted condition of the evaporator 18. The condenser fan motor is also energized when the compartment thermostat 32 closes since line 38 is connected to one side of the motor, and the other side of the motor is connected to side 36 of the power source.

After the condenser fan motor 30 has accumulated a predetermined amount of running time (corresponding to an expected defrost need), the control switch 28 is driven by the motor from its refrigeration position to its alternate defrost position. The defrost circuit will then be energized through the control switch 28 in its defrost position, line 48 connecting the switch 28 to the defrost heater 24, and line 50 connecting the defrost heater to the one side of the closed defrost thermostat 26 which has its other side connected to power side 36. When the switch 28 is moved to its defrost position, the compartment fan motor 30 and the compressor motor 14 are deenergized by loss of their connection to power side 34 through switch 28. After sufficient heat has been generated by the energized defrost heater 24 to defrost the evaporator 18, the defrost thermostat 26 opens and deenergizes the heater.

The refrigeration-defrost switch 28 will remain in its defrost (broken line) position with the compressor motor 14 and compartment fan motor 46 remaining deenergized until the control switch is returned to a refrigeration position. The switch 28 is returned to its refrigeration position by the further accumulation of running time 'of the condenser fan motor 30, which is energized directly through the compartment thermostat 32. It will be appreciated that if a defrost cycle begins in the refrigerator storage compartment when the temperature is sufficiently low that the thermostat 32 is open, then the heat generated by the defrost cycle will rather quickly cause the thermostat 32 to close and energize the condenser fan 30.

As an example of the duration of the time periods during which the condenser fan motor holds the control switch 28 in a refrigeration position, and alternately in a defrost position, the gear arrangement may be designed so that six hours of condenser fan motor operation constitutes a complete cycle and, of this six hours, approximately 20 to 25 minutes in one segment will be with the control switch in a defrost position. Since it may be expected that a defrost of the evaporator can be accomplished in, say, 7 to 10 minutes, this leaves a period of 15 to 18 minutes during which the pressures in the refrigeration system can move towards equalization.

One distinct advantage of the arrangement is that critical time tolerances in the periods during which the control switch is moved into and out of the defrost position are avoided. No problem exists of the fan motor carrying the switch through the defrost position and back to a refrigeration position. Since the movement of the switch 28 out of defrost is not a function of the termination of defrost, the requirement of only momentary energization of a compartment fan is avoided.

Another advantage of the arrangement of this invention 'over the Harbour arrangement is that if the defrost thermostat fails in a closed position, during the defrost operation, the defrost cycle will not continue indefinitely since the return of the control switch 28 to a refrigeration position is independent of the functioning of the defrost thermostat 26.

After the refrigeration-defrost control switch 28 has returned to a refrigeration position, the compressor will begin operation along with the compartment fan, while the condenser continues its operation under the control of the compartment thermostat. However, the compressor is not required to start against an undue load due to a high temperature and pressure in the evaporator and normal refrigerating operation continues under the control of the compartment thermostat until the condenser fan has again accumulated sufficient time to move the control switch 28 to its defrost position for another defrost cycle.

I claim as my invention:

1. In a refrigeration device having a refrigerated compartment; a compartment thermostat; a refrigeration system including a compressor, condenser, and evaporator; an electrical power source; means for defrosting said evaporator; a defrost termination thermostat; an evaporator fan for circulating compartment air through said compartment and over said evaporator; and a condenser fan; the improvement comprising:

a refrigeration-defrost control switch connecting said compressor and said evaporator fan for concurrent energization in a refrigeration position of said switch, and connecting said defrost means for energization in a defrost position of said switch, said switch being driven to alternate refrigeration and defrost positions by accumulated running time of said condenser fan; and

v 6 means connecting said condenser fan to said electrical energization of said defrost heater when said control power source for energization through said compartswitch is operated to said defrost position, said dement thermostat independently of the position of said frost circuit being opened by said. defrost thermostat control switch and the condition of said defrost terresponding to a defrosted condition of said evaporamination thermostat. 5 tor; 2. In a refrigeration device according to claim 1: a condenser fan circuit connecting said condenser fan said compressor and said evaporator fan are connected means to said power source through said compartin parallel between said control switch and one side ment thermostat for energization of said condenser of said power source. fan means in accordance with the position of said 3. In a refrigeration device having a refrigerated com- 10 compartment thermostat; partment; a refrigeration system including compressor whereby energization of said compressor and compartmeans, condenser and evaporator; compartment fan means ment fan circuit is controlled in accordance with the for creating flow of air over said evaporator compartaccumulated running time of 'said condenser fan ment; condenser fan means for creating a flow of air over means and independently of the condition of said desaid condenser; a compartment thermostat; a defrost frost thermostat so that under normal operating conheater associated with said evaporator; a defrost thermoditi'ons a sufficient time lag of the return of the constat having a normally closed position in response to a trol switch from a defrost position to a refrigeration chilled condition of said evaporator and operable to an position is obtained to avoid imposing an undue load open position in response to a defrosted condition thereof; upon said compressor at restart.

an electrical power source; the improvement comprising:

a refrigeration-defrost control switch driven to alternate References Clted refrigeration and defrost positions by accumulated TED STATES PATENTS running time of said condenser fan means; 2,662,330 12/1953 Sutton a compressor and compartment fan circuit, including 3,029,611 4/1962 Kuhn said compressor means and said compartment fan 3,063,250 11/1962 Moorman 62 155 means in parallel, connected to said control switch for energization when said control switch is in said MEYER PERLIN, Pl' Emmlllerrefrigeration position;

a defrost circuit connecting said defrost heater and defrost thermostat in series to said control switch for 62--157, 2 34 

